Guide to Analysis of Interference between Co-site
CDMA2000-800MHz and GSM-900MHz Base Station SystemsPlease enter the
document No.
Huawei Technologies Co., Ltd.
Document No.VersionSecret Level
Project Name:24 Pages in Total
Guide to Analysis of Interference between Co-site
CDMA2000-800MHz and GSM-900MHz Base Station Systems
(For Internal Use Only)
Prepared by:Antenna Feeder TeamDate:2002/07/31
Reviewed by:Date:yyyy/mm/dd
Reviewed by:Date:yyyy/mm/dd
Approved by:Date:yyyy/mm/dd
Huawei Technologies Co., Ltd.
All Rights ReservedRevision Record
DateRevised VersionDescriptionAuthor
2002/04/15V1.0First draft finished.Antenna Feeder Team
2002/07/31V2.0ModifiedAntenna Feeder Team
Table of Contents51 Foreword
2 Relevant Specifications for CDMA2000 1x/IS95A & GSM900MHz
Base Station Systems52.0 2.1 Relevant Specifications for CDMA2000
1x 800MHz BTSS52.152.1.1 Frequency band52.1.2 Specifications for
out-band spurious emission52.1.3 Blocking specifications52.1.4
Front end of receiver intermodulation specifications62.2 Relevant
Specifications for GSM 900MHz BTSS62.2.1 GSM frequency band62.2.2
Spurious emission specifications62.2.3 Intermodulation
specifications62.2.4 Blocking specifications73 RF Front-end Modules
Structure and Filter Feature Specifications of CDMA2000 & GSM
BTS73.1 CDMA2000 Front-End Module83.1.1 CDMA2000 CDU-800MHz83.1.2
CDMA2000 DDU-800MHz93.2 GSM900MHz CDU Front-End Module104
Interference Analysis104.1 Analysis of Interference between
CDMA2000 and GSM900 Systems114.1.1 Analysis of Interference of
System GSM900MHz by System CDMA2000114.1.2 Analysis of Interference
of System CDMA2000 by System GSM900MHz125 Analysis and Calculation
of the Influence of Interference on Receiver Sensitivities of GSM
and CDMA2000 Systems135.1 Equivalent Noise Level Analysis136
CDMA2000 1x (800MHz) and IS95A BTSs Co-site Interference analyze147
Antenna Isolation Calculations167.1 Horizontal Antenna Isolation
Calculation167.2 Vertical Antenna Isolation Calculation197.3
Calculation of Antenna Gain in any Direction20
Guide to the Analysis of Interference between Co-site
CDMA2000-800MHz and GSM-900MHz Base Station Systems
Keywords: spurious emission, intermodulation, blocking, receiver
sensitivity, antenna, isolation, interference
ABTStract: This document analyzes the interference between
co-site CDMA2000-800MHz and GSM-900MHz base station systems through
spurious emission, intermodulation and blocking, and sets forth
specifications for the mounting of base station antennas on the
basis of the analysis.
Abbreviations:
PA: Power Amplifier
LNA: Low Noise Amplifier
TTA: Tower Top Amplifier
List of References:
List of References
ArticleAuthorDocument No.Release DateBy what means to get the
articlePublisher
Digital Cellular Telecommunications System Phase (2+)
(GSM 05.05)
1 Foreword
As more new operators emerges and more new mobile communication
systems are put into use, multiple different mobile communication
systems are more frequently located at the same site. Due to the
close distance between antennas of a co-site system, interference
will occur between different systems. So to avoid this kind of
interference becomes an imminent issue. This kind of interference
(or blocking) is resulted from the antenna of a system receiving
unwanted (spurious, intermodulation) signals transmitted from
another co-site system antenna. This document analyzes this
interference in detail, and concludes the mounting specifications
of co-site antenna between CDMA-800MHz and GSM-900MHz by
calculation (or test data). This specification can serve as a guide
or suggestion for the mounting of co-site antennas.
2 Relevant Specifications for CDMA2000 1x/IS95A & GSM900MHz
Base Station Systems
Based on the relevant Protocol Specifications for base station
systems, the interference between co-site systems can be analyzed
through the spurious emission, intermodulation and blocking of
receiver.
2.1 2.1 Relevant Specifications for CDMA2000 1x 800MHz BTSS
2.1.1 Frequency band
Tx: 869--894MHz
Rx: 824--849MHz
2.1.2 Specifications for out-band spurious emission
Table 1 Spurious emission specifications in the CDMA 2000 1x
protocol
Frequency BandSpurious Emission SpecificationsRemark
9kHz--150kHz-13dBm/1kHz
150kHz--3MHz-13dBm/10kHz
30MHz--1GHz-13dBm/100kHz
1GHz --12.75GHz-13dBm/1MHz
2.1.3 Blocking specifications
Table 2 Blocking specifications Offset from center
frequencyInterfering signal levelWanted signal levelType of
interfering signalRemark
750kHz-67dBm-117dBmCWFor class 0
900kHz-30dBm-117dBmCWFor class 0
2.1.4 Front end of receiver intermodulation specifications
Table 3 Front end of receiver intermodulation specifications
Interfering signal levelOffset from center frequencyType of
interfering signal
-45dBm900kHzCW signal
-45dBm1700kHzCW signal
2.2 Relevant Specifications for GSM 900MHz BTSS2.2.1 GSM
frequency band
Tx: 935--960MHz
Rx: 890--915MHz
2.2.2 Spurious emission specifications
Table 4 GSM spurious emission specifications
Frequency BandSpurious Emission Specification
9KHz-1GHz-36dBm
1805-1880MHz-47dBm
1-12.75GHz-30dBm
2.2.3 Intermodulation specifications
I. Transmitter intermodulation specifications
Table 5 Intermodulation specifications for a GSM transmitter
Frequency BandSpecification
935-960MHz-36dBm (or 70dBc)
890-915MHz-98dBm
II. Receiver intermodulation specification
Front end of receiver unwanted signal level: (-43dBm
2.2.4 Blocking specifications
Table 6 GSM 900MHz band blocking specifications
Table 7 GSM 900MHz band blocking specifications
3 RF Front-end Modules Structure and Filter Feature
Specifications of CDMA2000 & GSM BTS
The front-end module in a CDMA2000 or a GSM BTSS has filters (or
duplexer) for transceiver channels, which suppress outgoing
spurious signals, incoming out-band signals and interference
between Tx and Rx signals in the system, etc. The CDMA2000 BTSS
working bands are as follows:
Tx: 870--880MHz
Rx: 825--835MHz
3.1 CDMA2000 Front-End Module
3.1.1 CDMA2000 CDU-800MHz
The CDMA2000 CDU-800MHz front-end module structure is as shown
in Diagram 1. Diagram 1 CDMA2000 CDU-800MHz front-end module
structure
The suppression index for Tx filter of various frequency bands
are shown in Table 8 .
Table 8 Tx filter specifications of a CDMA2000 CDU/800MHz
Frequency bandAttenuations (dBc)Remarks
9~150kHz30
150kHz~30MHz30
921~960MHz44
824~849MHz95
Other band in 30~1000MHz30
1710~1785MHz103
1805~1880MHz44
1880~1920MHz85
1920~1980MHz85
2010~2025MHz73
Other band in 1000~2105MHz17
2110~2170MHz44
2180~12750MHz30
3.1.2 CDMA2000 DDU-800MHz
The composition of a CDMA2000 DDU-800MHz is illustrated below in
Diagram 2, and signal attenuation specifications of the Tx duplexer
within various frequency bands are listed in Table 9 below.
Functional block diagram of a CDMA2000 DDU-800MHz
Table 9 Tx Duplexer specifications of a CDMA2000 DDU/800MHz
Frequency bandAttenuations (dBc)Remarks
9~150kHz23
150kHz~30MHz23
890~909MHz70
909~915MHz80
921~960MHz44
824~849MHz95
Other band in 30~1000MHz23
1710~1785MHz103
1805~1880MHz34
1880~1920MHz73
1920~1980MHz85
2010~2025MHz73
2110~2170MHz44
Other band in 1000~12750MHz17
3.2 GSM900MHz CDU Front-End Module
The composition of a GSM900MHz CDU front-end module is
illustrated below in Diagram 3, and signal attenuation
specifications of the Tx duplexer within various frequency bands
are listed in Table 10 below. The duplexer specifications of an EDU
are basically the same as those of a CDU.
Diagram2 Block diagram of a GSM900MHz CDU
Table 10 Tx duplexer specifications of a GSM900MHz CDU
Frequency bandAttenuations (dBc)Remarks
9KHz ~ 885MHz 40 dB
890MHz ~ 915MHz 95 dB
1000MHz ~ 1705MHz 40 dB
1710MHz ~ 1785MHz 95 dB
1805MHz ~ 1880MHz 75 dB
1920MHz ~ 3GHz 62 dB
3-6GHz 50 dB
6-12.75GHz 40 dB
4 Interference Analysis
Here below is the analysis of interference between two different
co-site base station systems, on the basis of their protocol
specifications described in section 2. Please note that none of the
calculations below involves any insertion losses (mainly including
module insertion losses and feeder losses), because the total
insertion loss varies according to actual lengths of feeder cables.
However, the total insertion loss can be taken as an isolation
margin.
4.1 Analysis of Interference between CDMA2000 and GSM900
Systems4.1.1 Analysis of Interference of System GSM900MHz by System
CDMA2000I. Rx in-band spurious interference analysis
If a spurious signal radiating from system CDMA2000 out of band
890--915MHz falls within the Rx working frequency band of system
GSM900MHz, the CDMA2000 system would interfere the GSM900MHz
system.
The equivalent noise level of a GSM receiver is required to be
-113dBm/200k (the GSM protocol requires that the BTS receiver
sensitivity be -104dBm with the carrier-interference ratio being
9dB). Hence, The level of the Rx in-band unwanted signal must be
less than -120dBm/200k (with a 7dB margin added). As a result, the
level of the out-band signal spurious emission from system CDMA2000
within the Rx working frequency band of system GSM900MHz must be
less than -120dBm/200k. The level of the out-band signal emitting
from Huawei system CDMA2000 power amplifier within the working
frequency band of system GSM900MHz is -26dBm/100k (-23dBm/200k).
And the suppression of Huawei CDU is greater than 56dB within band
890-915MHz while the suppression of Huawei DDU is greater than 70dB
within band 890-915MHz. In the case of Huawei CDU, the antenna
isolation is required to be:
-23-56- (-120)=41dB;
In the case of Huawei DDU, the antenna isolation is required to
be:
-23-70- (-120)=27dB.2. Intermodulation interference analysis
According to the GSM protocol, the intermodulation interference
level from out-band of GSM900 transmitting band should be lower
30dB than the transmitter maximum power output (For GSM is 46dBm).
So the CDMA2000 BTS emitting level within GSM900 transmitting band
should be less than 45-30=15dBm (45dBm is the CDMA BTS maximum
power output). While the requirement of CDMA2000 BTS spurious
emission is -13dBm/100k, which is far less than 15dBm. The
intermodulation interference within transmitting band can be
ignored.
GSM protocols require that the interference level falling into
GSM receiver front-end should be less than 43dBm. Here considers
the interference from CDMA2000 transmitter with the maximum power
output 45dBm, so the system isolation is required to be:
45- (-43)=88dB
The antenna isolation calculation is based on the indexes of GSM
receiver front-end module. Because the diversity filter has the
lower suppression capability on out-band signal (65dB within
935-960MHz), this filter index is taken to calculate the antenna
isolation as follows: 88-65=23dBBecause the maximum spurious signal
strength of the CDMA2000 out-band is -13dBm/100k, which is far less
than the transmit power. The intermodulation interference within
receiving band can be ignored.
3. Blocking analysis
Highest requirements of Blocking level for GSM receiver are:
inband -26dBm, out-band: 8dBm.
Because the level of the spurious emission from system CDMA2000
within the GSM900 frequency band is -23dBm/200k, the antenna
isolation is required to be:
-23-(-26) = 3dBThe maximum power output of CDMA2000 BTS is
45dBm, and the out-band suppression of the GSM receiver is higher
than 65dB. The blocking calculation is based on the signal
transmitted from CDMA2000 system as follows:
45-65=-20dBm
Hence, GSM blocking caused by out-band CDMA signals is
ignorable.
4.1.2 Analysis of Interference of System CDMA2000 by System
GSM900MHzI. Rx inband spurious smission analysis
The equivalent noise level of CDMA receiver is -109dBm/1.23M
(with the Noise Figure being 4dB). When 11 dB is added as margin,
The interference level caused by spurious emission within the
receiving band is required less than or equal to
-120dBm/1.23M.According to protocol specifications, the level of
the spurious emission from GSM900MHz system within the CDMA2000
frequency band is less than or equal to -36dBm/3M.At present the
out-band suppression of GSM frond-end module duplexer within
CDMA2000 frequency band is actually greater than 98dB. Hence,
according to the power amplifier indexes (the suppression of the
amplifier on spurious emission is 70dBc), the spurious emission
level fall into the front-end of The receiver is 46-70-98=-122dBm;
therefore the required antenna isolation is:
-122-(-120)=-2dB
In other words, the CDMA2000 system shall not be affected even
if there is no isolation between antennas.
2. Intermodulation interference analysis
The intermodulation attenuation out of CDMA2000 transmitting
band is required to be less than 30dB. In other words, the
interference level is required to be less than 45-30=15dBm. The
spurious emission from GSM900MHz system within band 869-894MHz is
less than or equal to -36dBm/3M(-40dBm/1.23M), so the requirement
is met.
The intermodulation interference specifications of CDMA2000
receiver require that the interference level falling into the
frond-end of the receiver should be less than or equal to -45dBm.
Here considers the interference from GSM transmitter with the
maximum power output 46dBm, and the diversity filter of CDMA2000
CDU frond-end module has the lower suppression capability on
out-band signal (65dB within GSM transmitting band), so the system
isolation is required to be: ((46-65)-(-45)=25dB. The suppression
of CDMA2000 DDU front-end module within GSM transmitting band
exceeds 90dB, so it can be ignored.3. Blocking analysis
The blocking level specification for a CDMA2000 receiver is:
-30dBm (for both in-band and out-band signals).
The level of the spurious emission from the GSM system within
CDMA2000 receiving is less than or equal to -40dBm/1.23m, and
therefore the blocking caused by GSM spurious emission is quite
weak.
The maximum power output of GSM BTS is 46dBm, and the out-band
suppression of the CDMA2000 receiver is higher than 65dB. The
blocking calculation is based on the signal transmitted from GSM
system as follows:
46-65-(-30)=11dBm
5 Analysis and Calculation of the Influence of Interference on
Receiver Sensitivities of GSM and CDMA2000 Systems
5.1 Equivalent Noise Level Analysis
Suppose the Rx intermediate frequency bandwidth of BTS is Bw
(MHz), and the receiving noise figure of BTS is Nf (dB).
Then the equivalent noise level of the BTS receiver is:
No=-114+10log (Bw)+Nf (dBm)
Suppose the demodulation carrier-interference ratio of the BTS
receiver is C/I (dB).
The theoretical BTS receiver sensitivity is So=No+(C/I)m,
wherein the (C/I)m is the minimum carrier-interference ratio.
According to this equation, the equivalent noise level directly
affects the BTS receiver sensitivity, namely, with the equivalent
noise level increasing by 1dB, the BTS receiver sensitivity would
deteriorate by 1 dB.
Typical values of the above mentioned parameters of the current
GSM and CDMA (IS95, CDMA2000, WCDMA) systems are respectively
listed in the following table.
Table 1 Values of typical parameters of various mobile
communication systems
IF Bandwidth (Bw) (MHz)BTS Noise Figure
(dB)BTS Equivalent Noise Level (dBm)Minimum Demodulation
Carrier-Interference Ratio (dB)Theoretical Receiver Sensitivity
(dBm)
GSM0.24-1179-108
IS951.254-109-14-123
CDMA20001.254-109-16-125
WCDMA54-103-19-122
in most cases, the actual minimum demodulation
carrier-interference ratios are basically the same as those values
in the table.
The external co-channel spurious interference within the
receiving band is supposed to be additive white Gaussian noise. The
influence of this noise on the system is to be superimposed to the
previous equivalent system noise level, and to increase the
receiving noise level. Listed in the following table are values of
the system receiver equivalent noise level raised under influences
of several noise levels (all in dB).
Table 2 Influence of noise levels on the equivalent system noise
level
The noise level is less than equivalent system noise level in
dB201612109630
The total noise level increases in dB after the external noise
interfering 0.040.10.370.40.50.971.763
the receiver sensitivity deteriorates in dB after the external
noise interfering0.040.10.370.40.50.971.763
According to the above table, if the previous receiver
sensitivity is allowed to deteriorate by 0.5dB, the permissible
noise level must be 9dB less than the previous equivalent system
noise level; if the previous receiver sensitivity is allowed to
deteriorate by 0.1dB, the permissible noise level must be 16dB less
than the previous equivalent system noise level; and if the noise
level is equal to the previous equivalent system noise level, the
receiver sensitivity would deteriorate by 3dB.
Taking a GSM BTS as an example, here below is the calculation of
the permissible external noise level.
According to GSM0505 protocol specifications, the sensitivity of
a GSM BTS receiver must excel -104dBm. If the minimum signal
demodulation carrier-interference ratio is 9dB, the equivalent
receiver noise level would then be -113dBm. Suppose at the
frond-end of the receiver there is now an external noise with a
noise distribution similar to a white noise. If the previous GSM
receiver sensitivity is allowed to deteriorate by 3dB, the noise
level can be equal to the previous equivalent receiver noise level,
i.e. 113dBm. If the receiver sensitivity is allowed only to
deteriorate by 0.5dB, the noise level must be 9dB less than the
previous receiver noise level, i.e. -122dBm/200KHz. If the receiver
sensitivity is allowed only to deteriorate by 0.1dB, the noise
level must be 16dB less than the previous receiver noise level,
i.e. -129dBm/200KHz.
6 CDMA2000 1x (800MHz) and IS95A BTSs Co-site Interference
analyzeInterference analysis of CDMA2000 and IS95 co-site mainly in
cases of these configurations mainly includes the following three
cases:
(1) Influence of the BTS transmitting with f1 on the BTS
receiving with f2;
(2) Influence of the BTS transmitting with f1 on the MS
receiving with f2;
(3) Influence of the MS transmitting with f2 on the BTS
receiving with f2.
There are two cases that CDMA2000 BTS and IS95 BTS work with
adjacent frequencies. The first is they both have two carriers with
the same two adjacent frequencies f1and f2 respectively. The
another is CDMA2000 BTS works with f1 and IS95 BTS works with
f2.
Case 1: Influence on BTS receivers itself when this BTS works
with adjacent frequencies f1 and f2
In this case, at least two TRXs are configured with a sector,
respectively working with frequency f1 and f2. Because each carrier
must ensure the -117dBm receiver sensitivity, the spurious emission
of each carrier falling within the BTS Rx frequency band is at
least less than -110dBm to guarantee the receiver sensitivity.
Hence, interfering sources are mainly the dividers crosstalk and
inter-transmitter intermodulation. As for the dividers crosstalk,
because full consideration has been given to the crosstalk issue
during system designs, and there are specifications for the in-band
spurious emission of each TRX and for the isolation of the dividers
port. This issue is nonexistent (the receiver sensitivity and other
receiving specifications must be complied with). As for the
inter-transmitter intermodulation, because the duplex space between
Tx and Rx in CDMA800MHz system is 45MHz, and the intermodulation of
two frequencies at an interval of 1.23MHz, falling into the Rx
frequency band, is already below order 45, the intermodulation of
adjacent frequencies can be ignored.Conclusion: No influence,
ignorable.Case 2: Influence on BTS receivers when different BTSs
work respectively with adjacent frequencies f1 and f2In this case,
BTS A works at f1 and has its own transmitting & receiving
antenna, while BTS B works at f2 and has another transmitting &
receiving antenna.(1) Co-channel spurious interference of
receiversAccording to specifications for CDMA base station systems,
the maximum level of the out-band spurious emission of a
transmitter is in theory -13dBm/100KHzRBW (equivalent to
-3dBm/1MHzRBW). If this spurious signal falls within the Rx
frequency band, it would severely interferes the receiver of
another BTS. To ensure the minimum 117dBm receiver sensitivity, the
spurious signal level of the transmitter, falling into the
front-end of receiver within the Rx frequency band, is definitely
less than -110dBm.
Suppose the BTS receiver sensitivity is the typical
-123dBm/1MHzRBW, and its equivalent receiver noise level is
-109dBm/1MHzRBW. If the receiver sensitivity is allowed to
deteriorate by 3dB, the permissible co-channel interference level
is-109dBm/1MHzRBW.
Hence, the requirement for the isolation between the
transmitting antenna of one BTS and the receiving antenna of
another is: the relative net gain being no greater than 1dB.
(2) Blocking of receivers
According to specifications for CDMA base stations, the receiver
blocking level is required to be at least -30dBm (for both in-band
and out-band signals). To comply with this specification, BTS must
have a Tx/Rx isolation of more than 80dB at least. In other words,
the level of the Tx signal falling into the receiver must be less
than -30dBm. Because the Tx/Rx working frequency bands of the two
BTSs are completely identical with each other, Tx/Rx isolation
between different BTSs is complied with each other. Hence, the
blocking issue is nonexistent so far as there is no net gain
between antennas of the two BTSs (e.g. none face-to-face
emission).
Conclusion: Because the Tx/Rx working frequency bands of the two
BTSs are completely identical with each other, and both comply with
the same protocol specifications, the blocking is nonexistent so
far as there is no net gain between antennas of the two BTSs due to
a face-to-face emission.
Case 3: Influence on the MS receiving when adjacent frequencies
f1 and f2 are employed for one same sector.
The following two interference cases should be considered.
(1) Co-channel receiving interference
According to CDMA specifications, the receiving sensitivity of
CDMA MS is required to be no worse than -104dBm/1MHz. If the
receiving noise figure is the typical 7dB, the equivalent noise
level would be -97dBm/1MHz. If the receiving sensitivity is allowed
to deteriorate by 3dB, the permissible co-channel interference
level is -97dBm/1MHz.
There is an ACPR (Adjacent Channel Power Ratio) for each CDMA
BTS carrier (less than 45dBc if the offset from the center
frequency is 750KHz, and less than 60dBc if the offset from the
center frequency is 1.98MHz). If two adjacent frequencies are
employed for one cell, because the SNR of the signal arriving at a
MS would be more than 45dB, the interference level of the f2 signal
received by a MS working at f1 would be far less than 97dBm, thus
not resulting in co-channel interference.
(2) Blocking interference
The MS receiving level is required within the range from -20dBm
to its sensitivity. If the received signal level exceeds 20dBm, the
MS may be blocked.
As analyzed in (1), if the two adjacent frequencies are employed
for one cell, because there is almost no difference in propagation
loss between them, it is impossible that the f1 signal would block
the MS working at signal f2.
But, if the two adjacent frequencies come from two different
cells, and the MS has been restricted to a certain working
frequency, it is possible that the MS may be blocked by the invalid
frequency signal.
Conclusion: If a MS is able to select the stronger signal to get
online, the interference issue is nonexistent. If MS has been
restricted to one certain working frequency, and the location of
the MS is within the coverage area of an invalid signal, the MS may
not be able to get online.
7 Antenna Isolation Calculations
In this section, equations used to calculate the antenna
isolation based on the antenna gains and mounting distance between
antennas are given..
7.1 Horizontal Antenna Isolation Calculation
Here below are values of relative gains of antenna emissions at
various angles.
The angle of the antenna beam in the direction of maximum
emission is defined as 0. Relative gains of antenna emissions at
different angles in column Angle a, with reference to the gain in
the direction of maximum emission, are listed below in Table 13
(which applies to all 824-960MHz BTS antennas. When angles are
greater than 90, relative gains of antennas in similar types made
by different manufacturers may have an error of about 3dB):
Table 3 Relative gains of antenna emissions at different
angles
Angle a6590120
00 (dB) same below0 (dB) same below0 (dB) same below
5-0.100
10-0.3-0.2-0.1
15-0.7-0.4-0.2
20-1.2-0.7-0.3
25-1.9-1.1-0.5
30-2.7-1.5-0.7
35-3.6-2-0.9
40-4.6-2.6-1.2
45-5.8-3.3-1.6
50-7-4-2
55-8.3-4.8-2.4
60-9.7-5.7-2.9
65-11.2-6.6-3.5
70-12.6-7.6-4.1
75-14-8.6-4.7
80-15.4-9.7-5.5
85-16.5-10.8-6.3
90-17.6-11.9-7.1
95-18.5-12.8-7.8
100-19.5-14-8.5
105-20.5-15.3-10.1
110-21.5-16.7-11.7
115-22.4-18.3-14.2
120-23.5-20-16.5
125-24.7-21.8-18.6
130-26.8-23.4-20
135-27.7-25-21.6
140-29.2-26.2-22.9
145-30.1-26.6-22.9
150-31.6-26.4-22.7
155-30.5-26.1-22.5
160-30.8-26-22.4
165-29.9-26.3-22.7
170-28.8-26.4-22.9
75-27.9-26.4-23.0
180-27.0-26.4-23.1
With the above data, following equations can be used to
calculate the isolation between two antennas.
When two antennas are placed in the horizontal direction, the
isolation between them depends upon their emission patterns,
distance between them and gains. The gain in the direction of
maximum emission of antenna 1 is G1 (dBi), and the level of the
side lope at angle a1 is SL1 (in dBp, a negative value relative to
the gain of the main beam). The gain in the direction of maximum
emission of antenna 2 is G2 (dBi), and the level of the side lope
at angle a2 is SL2. The horizontal distance between the two
antennas is d. a1 is the angle from the line in the direction of
maximum emission of antenna 1 to the connecting line between
antenna 1 and antenna 2, a2 is the angle from the line in the
direction of maximum emission of antenna 2 to the connecting line
between antenna 2 and antenna 1. Then, the horizontal isolation
between antennas is:
HI=-22-20log(dh/ (dB) (negative value)........(1)
If they are both omnidirectional antennas, SL1=SL2=0(dB).
Variable in the above equation stands for working wavelength
(similar to the far field analysis).
Equation 1 is applicable under far field conditions. The
distance between the two antennas must meet the following
requirement (in which case, the error is about 0.5dB):
dh>((L1+L2)2/); wherein, L1 and L2 are respectively the
maximum sizes of the two antennas.
If the distance between them is close, the HI calculated by
means of equation 1 has a relatively great error (about 6-10dB less
than the HI actually measured). Please refer to Antenna Isolation
Test and Analysis.Examples:
Example 1: There is an omnidirectional antenna (900MHz, 11dBi)
and a directional antenna (900MHz, 65, 18dBi); the distance between
them, d, is 300m; a=60. Here below is how we calculate the
isolation between the two antennas. The antennas are placed as
illustrated below in Figure 5.
Figure 2 Relative positions of the omnidirectional and
directional antennas
Therefore, G1=11, SL1=0, dh=300, G2=18, SL2=-9.7 (found in Table
13 above), =300/947.5=0.317. Substitute variables in equation 1
with these values:
HI= -22-20log(dh/ = -22-20log(300/0.317)+(11+18)+(0-9.7) = -62.2
(dB).
Hence, the antenna isolation is 62.2dB.
Example 2: There is a directional antenna (900MHz, 90, 15dB) and
another (900MHz, 120, 15dBi); the distance between them, d, is
300m; a1=90; a2=60. Here below is how we calculate the isolation
between the two antennas. The antennas are placed as illustrated
below in Figure 6.
Figure 3 Relative positions of the two directional antennas
Therefore, G1=15, SL1=-11.9 (found table 17 above), dh=300,
G2=15, SL2=-2.9 (found in Table 13 above), =300/947.5=0.317.
Substitute variables in equation 1 with these values:
HI = -22-20log(dh/ = -22-20log(300/0.317)+(15+15)+(-11.9-2.9) =
-66.3 (dB).
Hence, the antenna isolation is 66.3dB.
Example 3: there is a directional antenna (1800MHz, 65, 15dBi)
and another (1800MHz, 65, 15dBi); the distance between them, d, is
300m; a1=90; a2=60. Here below is how we calculate the isolation
between the two antennas. The antennas are placed as illustrated
below in Figure 7.
Figure 4 Relative positions of the two directional antennas
Therefore, G1=15, SL1=-11.9 (found in Table 13 above), dh=300,
G2=15, SL2=-2.9 (found in Table 13 above), =300/1842.5=0.163.
Substitute variables in equation 1 with these values:
HI= -22-20log(dh/= -22-20log(300/0.163)+(15+15)+(-11.9-2.9)=
-72.1(dB).
Hence, the antenna isolation is 72.1dB.
7.2 Vertical Antenna Isolation Calculation
If two BTS antennas are mounted on the same tower but different
levels, they are placed in the vertical direction. The following
equation is used to calculate the isolation between two antennas in
the vertical direction and aligned (see the diagram on the left in
Figure 8):
VI=-(28+40log(dv/))+(g1+g2) dB ........(2).
Herein, g1 stands for the gain of antenna 1 in the direction of
antenna 2, while g2 stands for the gain of antenna 2 in the
direction of antenna 1. Usually, the approximate value, g1=g2=0dBi,
can be assumed.
The following equation is used to calculate the isolation
between two antennas in the vertical direction but not aligned (see
the diagram on the right in figure 8):
SI=(VI-HI)angle/90+HI .......... (3)
Figure 5 Relative positions of two antennas Placed in the
vertical direction
7.3 Calculation of Antenna Gain in any Direction
During the interference analysis, we usually wish to know what
is the antenna gain in a certain direction, but antenna suppliers
in most case only provide the horizontal and vertical emission
patterns. If a point is located on neither the horizontal nor the
vertical patterns, the following equation, equation 4, can be used
to calculate the antenna gain at this point.
Suppose the antenna gain is G (dBi), and the normalized
horizontal and vertical emission patterns of the antenna are
illustrated below in Figure 9. The following equation can be used
to calculate the gain at point P. The location of Point P in the
horizontal direction is illustrated in the diagram on the right in
Figure 9.
G (p)=G+10log (10eh/1010ev/10); wherein, ev is the vertical
emission pattern normalized value (-dB)
=G+10log (10-3/1010-10/10)=G-13 (dB); wherein, eh is the
horizontal emission pattern normalized value (-dB).
Figure 6 Emission patterns of the antenna
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